@William K.: Phase separation occurs at about 0.5% moisture for E10 fuel (i.e. gasoline with 10% ethanol) at 70°F, according to the document I linked to. Like you say, gasoline with higher ethanol contents, such as E15, can tolerate a lot more moisture before phase separation occurs. This is one of the concerns about moving to E15, and one of the reason why longer-chain alcohols such as butanol are being investigated as alternatives.

You can read about some exciting current work on biobutanol in marine applications here.

I don't buy any ethanol mixed gasoline. It seems to reduce gas mileage and caused deer corn to cost a lot more, plus corn crops are a failure this year. So, I don't expect and price cuts at the pump. My gas powered lawn equipment is going through its first massive drought summer and has operated fine all three times I used it. It advertises that it will operate with ethanol 10% max mix. 10% ethanol in a premium fuel car doesn't work well at all. Fuel in your oil sounds like a different issue like not changing the oil often enough or bad float height or float valve seat. Rarely have I ever had to change a plastic float and if it used a brass float, you usually can still get one made of brass. Maybe not at your local auto parts store, but they are out there.

Loadstar, I have a "toy" yard, so I actually use a manual push mower. It is very like my childhood when I earned $$ mowing large yards with push mowers. Given my toy yard, my electric weedeater will last decades. So no complaints here.

Two relevant things to this issue.1. There are so many things put in gasoline these days between alcohol and the entire hydrocarbon spectrum, its almost impossible to figure what might have caused early degradation of the primer bubble. If you get five years out of a $60 weedeater, it owes you nothing. Mine seems to take the worst from UV if I don't put it away and out of the sun. Electric weedeaters are toys good for toy-size yards.

2. Parts. B. S. supposed that a weedeater engine doesn't change or evolve. I challenge her to explore the parts breakdowns at sears or repairclinic.com and revise her worldly view of small engine repair. I counted five iterations of a primer bulb for weedeater carbs in one search iteration. Almost all Briggs & Strattons have slightly different production runs. Some common. Some not.

Nothing lasts forever. Having mega stores contributes to the convenience of cheap stuff. Stop whining about the government. If we didn't have gas, we'd all be busy herding sheep or on our knees from exhaustion of using manual mowers. And we wouldn't have all this spare time to spew electronic drivel on how tough life is.

Something is missing in the explanation about moisture separateion. Like, what concentration of alcohol are they referencing the moisture separating at 0.5% concentration. Certainly the amount of water that can be disolved depends a whole lot on the amount of alcohol in the mix. That is sort of intuitive.

Of course, that is only with nice grain alcohol, it does not include the less pure stuff, nor is that including the methyl alcohols.

And now ifrared spectometry can be donefast and cheap if only one target is sought, and that target is well understood. BUt I was thinking of something fast and cheap and simple. So the short answer becomes "probably not".

@William K.: Actually, I was way off with the 6% number. At 70°F, phase separation occurs when the moisture content exceeds about 0.5%. This document will tell you more than you ever wanted to know about phase separation.

Real-time, in-line measurement of moisture content in gasoline might require infrared spectroscopy, which probably wouldn't be cheap. Maybe there is a cheaper way to do this, but I can't think of one.

Dave, the points you make are certainly valid, but the hardware for measuring density is a lot more involved than for measuring resistance. My idea was for the measurement system to be integral with the fuel pickup assembly located in the gas tank, so that an immediate indiaction would be available if the gas being purchased contained water and alcohol. That would allow me to stop and avoid filling the tank with the poor quality fuel. Also, the response could be quite fast.

Are you sure that the separation threshold is only 6% water? I thought that it was about equal to the percentage of alcohol?

@William K.: I agree that you should (in principle) be able to measure the water content of a gasoline-ethanol mixture by conductivity, but I haven't been able to find any references on the Internet to anyone actually doing this. The overall conductivity may be too low to measure reliably.

Another way (in principle) would be by measuring the density, except that the density of gasoline itself can vary by too much to make this measurement meaningful.

You could also add water until you get phase separation. At room temperature, E10 will separate into two phases (gasoline and ethanol-water mixture) once the moisture content exceeds about 6% (edit: should be 0.5%, not 6%). So if get phase separation when you add 5% water, you know that the gasoline already contained 1% water.

Or you could combine the two approaches, by adding a known amount of water to deliberately cause phase separation, then measuring the density of the ethanol-water phase only.

By the way, the amount of water needed to cause phase separation decreases as the temperature decreases. We are just entering the time of year when phase separation often occurs in large storage tanks: the fuel absorbs water during the humid summer months, then undergoes phase separation in the fall as temperatures start to get cold.

What has been ignored by all parties is the "DryGas" effect, where adding ethanol to gasoline allows water to be disolved and run through the fuel system without the engine ceasing to operate. That used to be a problem when water would get into the fuel somehow.

The problem now is that sellers can add water to the gas and the cars will still run and only have a moderate loss of power. Of course, there is also a "moderate" drop in miles per gallon as well. The reason that this is a problem is that I don't want to be paying $4 per gallon for water, especially in my gas tank! Besides that, the added water will speed up the corrosion a bit on metals such as aluminum.

But nobody seems to be at all concerned about this problem, at least around this part of the state.

It seems like checking the conductivity of the mix ought to be a way to evaluate the proportion of water added, but I have not verified this.

A few weeks ago, Ford Motor Co. quietly announced that it was rolling out a new wrinkle to the powerful safety feature called stability control, adding even more lifesaving potential to a technology that has already been very successful.

It won't be too much longer and hardware design, as we used to know it, will be remembered alongside the slide rule and the Karnaugh map. You will need to move beyond those familiar bits and bytes into the new world of software centric design.

People who want to take advantage of solar energy in their homes no longer need to install a bolt-on solar-panel system atop their houses -- they can integrate solar-energy-harvesting shingles directing into an existing or new roof instead.

Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.